1. Field of the Invention
The present invention relates to synthesizing Cu(InxGa1-x)S2 and Cu(InxGa1-x)Se2 nanoparticles and, more specifically, to synthesizing these nanoparticles using flame spray pyrolysis.
2. Description of the Prior Art
Thin film chalcopyrite solar cell absorber layers of CuInSe2, CuInS2, Cu(InxGa1-x)S2, and Cu(InxGa1-x)Se2, or their mixtures, generally known as CIS or CIGS, have been investigated since the 1980's. They have efficiencies superior to CdTe and can be produced using non-vacuum technology, thus cutting down on costs. The record efficiency for a chalcopyrite based solar device to date is 19.9%, and the theoretical efficiency is about 30%. The band gap of these materials can be adjusted from 1.0-2.4 eV by controlling the ratio of In to Ga. Some of the methods to produce these materials have included coating inks onto substrates followed by a post deposition anneal in H2S, or H2Se, electro deposition of precursors, paste coating, and chemical spray pyrolysis. In many cases the precursors in these methods require the use of pyridine, a highly hazardous material. Furthermore, a difficulty for these processes is that it is difficult to obtain dense films, where a film thickness of 1-2 μm should be obtained.
Flame synthesis techniques are non-vacuum gas phase processes that have been shown to be very effective in producing high purity oxide nanoparticles on an industrial scale. In these processes precursor materials are either volatile, or are aerosolized by various means. Upon being sprayed, precursor droplets evaporate and undergo combustion in the flame. The aerosol species that are formed are rapidly quenched as they leave the reaction zone, leading to the formation of oxide nanoparticles.
A method for synthesizing Cu(InxGa1-x)S2 and Cu(InxGa1-x)Se2 nanoparticles using flame spray pyrolysis with a post deposition sulfurdization or selenization to form a solar cell absorber layer has never been demonstrated before. Other methods to synthesize CIGS nanoparticles require either expensive vacuum equipment, or many processing steps, often with harmful chemicals and application onto substrates with more time consuming and involved methods such as doctor blade techniques.